Not really any opening : the iron rule of the Salic Law means no cadet could go for the elder's throne. As much as Charles of Navarra wanted it, he was nowhere as the Yorks were to the Lancasters. Th only possibility would be a total extinction of the Bourbon in the 18th c. and a middle-ground pretender with alleged Capetian ancestry. Even in this case, a Valois or Bourbon bastard branch had more chances than a newcomer : the genealogical charts were accurate, and no "lost branch" existed. Even the Courtenay, who were denied their rights as princes, had a perfectly clear lineage.